em6324qysp5b-2.8 EM Microelectronic, em6324qysp5b-2.8 Datasheet - Page 10

• Manufacturer Part Number: em6324qysp5b-2.8
• Description: Reset Circuit With Manual Reset And Watchdog
• Manufacturer: EM Microelectronic

Watchdog Input
If the watchdog timer has not been cleared within t
(1.6s typ.), reset asserts. The internal 1.6s timer is
cleared by either a reset pulse or by toggling WDI. While
reset is asserted, the timer remains cleared and does not
count. As soon as reset is released, the timer starts
counting.
If the microcontroller I/O connected to WDI is put in a
high impedance condition, the circuit will detect this
condition as a microcontroller in sleep mode and prevent
its watchdog from timing out. To monitor a high
impedance or a three state condition on WDI, the
watchdog input is internally driven low during the first
15/16 of the watchdog timeout period and high for the
last 1/16 of the watchdog timeout period.
Copyright © 2006, EM Microelectronic-Marin SA
09/06 - rev.J
[ uA ]
V
RESET
WDI Input Current Low-level I
DD
15.0
12.0
9.0
6.0
3.0
0.0
t
POR
-50
-25
WDI Input Timing Diagram
WDI Pulldown ON
WDI Pullup OFF
0
(V
15/16 t
DD
25
=5.5V)
[ °C ]
WD
t
WD
50
IL
vs. Temperature
75
1/16 t
OFF
ON
100
WD
OFF
125
ON
Fig. 17
WD
Fig. 15
10
When WDI is left unconnected, this internal driver clears
the 1.6s timer every 1.5s. When WDI is three-stated or
unconnected, the maximum allowable leakage current is
0.5µA.
To minimized the overall system power consumption and
therefore for a minimum watchdog input current leave
WDI low for the majority of the watchdog timeout period,
pulsing it low-high-low once within the first 15/16 of the
watchdog timeout period to reset the watchdog timer. If
WDI is externally driven high for the majority of the
timeout period, up to 35µA can flow into WDI. Meanwhile
when the microcontroller is not in sleep mode, the output
of the microcontroller which drives WDI has to be strong
enough to fight the 35µA.
WDI
[ uA ]
GND
V
WDI Input Current High-Level I
25.0
20.0
15.0
10.0
DD
5.0
0.0
-50
WDI Input Stage Block Schematic
-25
15/16 t
1/16 t
0
(V
WD
WD
25
DD
EM6323/24
[ °C ]
=5.5V)
Pullup
Pulldown
www.emmicroelectronic.com
50
Transition
IH
Detector
75
vs. Temperature
100 125
Watchdog Logic
+ Timer
Fig. 18
Fig. 16